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ProRes 4444 alpha channel playback conundrum
(Moderators please feel free to move this post – I’m putting it here because my original workflow is in AE).
I’m doing some tests for an augmented reality project which is going to involve green screen video. Footage is full 4k (shot portrait). I did a multi level key in AE and exported test initially with Apple Animation codec.
I wanted to experiment with file sizes between different codecs that carry an alpha channel (using Media Encoder) including ProRes 4444 and DNxHR.
Both look fine when the resulting files are imported in to an NLE (Premiere for example) but the ProRes 4444 file seems to show enhanced green spill and bobbling when playing back in VLC or QT Player. I don’t get this with the Animation codec – it plays fine in both. I should point out that they key is not completely clean yet but shouldn’t look like it does on the left!. I’ve attached a screen grab showing the identical file playing in both QT Player (left) and Premiere CC17 (right).
Can anyone tell me what’s happening here?
Thanks in advance.
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4 Replies
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Hello Dave,
Thanks for the response. If that is the case though why does the Animation export display just fine in both VLC and QT Player but the ProRes 4444 version does not. I have attached an image (ProRes is on the left).
Thanks.
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What is your final destination? Taking it into an NLE? I would check there, not with a media player. Some may not show alpha channels, some may show premultiplied incorrectly, where you can see all the edge junk. Check in your NLE.
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Actually the Animation export from AE was premultiplied. The prores export was done through Media Encoder which doesn’t seem to have an option to select straight or premultiplied.
Whatever Media Encoder was doing seems to have been the problem. Exporting prores 4444 with premultiplied alpha (the default option) direct from from AE plays perfectly fine in QT Player.
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The destination is not quite straight forward as this is a test for an augmented reality project and the video will play via a bespoke smartphone app developed by another company – hence I’ve been trialling different codecs for final delivery. The media was fine in Premiere I was just curious as to what was causing the difference between the two codecs playing back in a media player.
It seems that Media Encoder is causing the issue in this instance (as I’ve mentioned in a post below). Exporting ProRes 4444 directly from the source media in AE with premultiplied alpha plays just fine in QT Player.
I can only assume Media Encoder does something with the alpha channel when transcoding. Shifting from premultiplied to straight? Just a guess…
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